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LabMaster 10 Zi Oscilloscopes
Response Optimization Modes
Frequency response and group delay of the oscilloscope contributes to the
pulse response characteristics of the oscilloscope. By slightly adjusting these
characteristics using digital signal processing, the characteristic response of
the oscilloscope can be optimized for your specific application.
Frequency response is defined as the decrease in the magnitude response
with respect to frequency. A fourth-order Bessel roll-off slightly attenuates
the frequencies near the bandwidth rating of the oscilloscope while a brick-
wall frequency response passes slightly higher frequency content.
Group delay is defined as the rate of change of the total phase shift with
respect to angular frequency through a device or transmission medium.
Amplifiers in analog oscilloscopes typically have some group delay at the
highest frequencies. This inherent group delay minimizes the preshoot
present on a step response and provides the traditional pulse response with
no preshoot before the step. When zero group delay is provided at all
frequencies, preshoot and overshoot is equalized.
Teledyne LeCroy provides three choices for response optimization. Each
combines a frequency and group delay response to optimize the
oscilloscope for particular applications.
Pulse Response. A group delay compensation minimizing
preshoot, this selection most resembles the response of an
analog oscilloscope by controlling group delay to be slightly
non-zero at the highest frequencies. In addition, a fourth-
order Bessel frequency response is implemented.
Eye Diagram. Flat group delay compensation resulting in
equalized preshoot and overshoot. This selection improves
the symmetry of serial eye diagrams. In addition, a fourth-
order Bessel frequency response is implemented.
Flatness. Flat group delay compensation with a brick-wall
frequency response. While this provides the fastest rise time,
there is also a slight penalty of more preshoot and overshoot
compared to Eye Diagram mode. This selection is most often
used in narrow-band RF measurements where it is desirable
to maintain constant magnitude response over the oscilloscope passband.
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922561-00 Rev A
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